THIS INVENTION relates to an improved crop and to a process for reducing plant losses or enhancing plant recovery following stress related procedures, including but not limited to transplanting or pruning procedures.
The success of ventures involving commercial use of plants including-fruiting plants involves risks. Risks arise as a consequence of many variables. These include inter alia, the weather, unexpected climatic variations, the quality of juvenile plants and timing of artificially induced events, such as planting in relation to anticipated seasonal events and so forth. Many of these variables cannot be quantified and where, for example, planting takes place too late or too early and say, anticipated seasonal changes do not occur as hoped, or adverse weather interferes with events, the yield from a crop can be adversely effected. A venture can become unprofitable.
It is known that yield can be improved in mature plants by a process known as pruning. While the yield of the pruned plant compared to the unpruned plant is increased, the yield is not necessarily maximised because the yield depends on the plant""s recovery from pruning induced stress. Similarly, where juvenile plants are transplanted, particularly where commercial numbers are concerned, plant losses occur as some plants cannot recover from the transplanting procedure. Moreover, recovery rates in a transplantation can be slow and this in turn can also effect overall yield. These problems are exacerbated in the large scale commercial environment as a 20% or even 10% reduction in yield from year to year can mean the difference between profit and loss.
At present, conditions considered appropriate to application of induced stress such as pruning or transplanting are evaluated on a qualitative basis having regard to, inter alia, season and visual appearance of plants. The applicant has found that the latter test can be deceptive insofar as assessing a plant""s ability to withstand artificially induced stresses, particularly those associated with transplanting.
It is therefore an object of the present invention to alleviate at least to some degree the aforementioned problems of the prior art.
In one aspect therefore, the present invention resides in a crop having on average an improved yield due to a reduced plant loss rate or enhanced plant recovery rate following transplanting, pruning or like stress related procedures, the crop comprising, a plurality of plants, the plants having been selected according to a representative sample of said plants being quantitatively confirmed as being in a relatively high stress tolerance phase, said selection being according to a measurable characteristic of the representative sample of said plants being indicative of the plants being in the relatively high stress tolerance phase, prior to the stress related procedure being carried out.
In a further aspect, the invention resides in a process for reducing plant loss or enhancing plant recovery after subjecting a plant to artificially induce stress such as transplanting operations, pruning operations or the like, the process comprising the steps of:
(a) prior to subjecting the plant to the artificially induced stress, quantitatively confirming that the plant is in a relatively high stress tolerance phase by determining the state of the plants"" energy according to a measurable internal characteristic of said plant, said measurable characteristic being indicative of the plant being in said relatively high stress tolerance phase; and
(b) subsequently subjecting the plant to the artificially induced stress before said plant enters a relatively low stress tolerance phase.
In another aspect, the invention resides in a culling process for eliminating a high proportion of plants having relatively low stress tolerance from a plurality of independent plant populations, each plant population comprising a plurality of plants which are of the same production lot from a specific source, the culling process comprising the steps of:
(a) selecting a representative sample of plants corresponding to each population;
(b) quantitatively ascertaining whether said representative sample of plants is in a relatively low stress tolerance phase or a relatively high stress tolerance phase by determining the state of the plants"" energy reserves according to a measurable internal characteristic of said plants in said sample being indicative of the plants"" tolerance to stress; and
(c) subsequently culling those populations of plants that correspond to the representative sample of plants which have been ascertained as being in a relatively low stress tolerance phase.
In a still further aspect, the invention resides in a process for preparing and selecting plants suitable for being subjected to artificially induced stress such as transplanting or pruning, the process including the steps of:
(a) selecting a representative sample of plants from a plant population, the plants of which are from the same production lot from a specific source;
(b) quantitatively ascertaining whether said plants in said representative sample are in a relatively high stress tolerance phase or a relatively low stress tolerance phase by determining the state of the plants"" energy reserves according to a measurable internal characteristic of said plants in said sample is said measurable characteristics being indicative of said plants being in a relatively low or a relatively high stress tolerance phase;
(c) where said plants in said sample are shown to be in a relatively low stress tolerance phase, select all said plants in said population as being substantially stress intolerant and set them aside as being unsuitable to be subjected to said artificially induced stress; and
(d) where said population has been set aside as being in a relatively low stress tolerance phase then subject said population to a process adapted to artificially induce a relatively high stress tolerance phase in said population;
(e) subsequently select a further representative sample from said population that has been subjected to said process adapted to artificially induce a relatively high stress tolerance phase;
(f) quantitatively ascertain whether said plants in said further representative sample have reached or have failed to reach an induced relatively high stress tolerance phase according to a measurable internal characteristic of said plants in said further representative sample, said measurable internal characteristic being indicative of a plant being in a relatively high or relatively low stress tolerance phase; and
(g) where said plants in said further sample are shown to be in a relatively high stress tolerance phase select all said plants in said population as having been successfully artificially induced into a relatively high stress tolerance phase as being substantially stress tolerant and set them aside as being suitable to be subjected to said artificially induced stress.
In a still further aspect, the invention resides in an apparatus suitable for quantitatively ascertaining whether a plant is in a relatively high stress tolerance phase or a relatively low stress tolerance phase, the apparatus having a plant sample receiving station and a readout means adapted to provide a direct readout of a measurable characteristic of said plant sample indicative of the plant from which said plant sample has been taken as being in a relatively high or relatively low stress tolerance phase. Preferably, the direct readout provides an average measure of a whole population of related plants tolerance to stress as an average mortality or recovery rate related figure indicative of the stress tolerance of the population derived from a sample located in said sample receiving station.
The present invention can be applied to any crops where it is desirable to optimise yield by firstly identifying and optimising the time at which plants are subjected to induced stress so that afterwards a relatively high recovery rate can be expected. The present invention can be applied to commercial strawberry production as an illustration.
In the life of a strawberry plant, it is subjected to artificially induced stress. For example, juvenile plants, known as runners, are purchased from runner nurseries and transplanted by the strawberry grower. The yield from a crop of strawberries depends on, inter alia, the time at which planting takes place and the strike rate. The strike rate is a measure of the percentage of runners surviving following transplanting. The strike rate is therefore a measure of the tolerance of the crop to the transplanting procedure, assuming that normal external factors are constant. Prior to the present invention, transplanting has been subject to sporadic variations in strike rate, sometimes strike rates as low as 80% are recorded despite the runners, from a visual point of view, being healthy and also disease free. The applicant has found that runners which are disease free and visually sound may not be able to cope with transplanting because these plants can be in a relatively low stress tolerance phase which reduces the probability of the plant surviving which in turn reduces strike rate and hence, yield.
In the second and sometimes following years from transplanting, mature plants are subjected to a process known as xe2x80x9cratooningxe2x80x9d where plants are cut-back or pruned. The yield depends on when ratooning takes place and how the plants recover from ratooning. The time at which and the amount by which plants are cut back is usually determined on a qualitative basis.
The present invention can also be applied to other commercial crop such as bananas and lychees.
As mentioned above, the processes disclosed herein and the apparatus mentioned above involve quantitatively ascertaining whether a representative sample of plants in a population is in a relatively low stress tolerance phase or a relatively high stress tolerance phase. The applicant has developed a procedure for ascertaining the stress tolerance phase of a plant, the preferred procedure in relation to strawberry plants and which can also be used for other plants involves ascertaining the xe2x80x9cTotal Dissolved Solidsxe2x80x9d (TDS) as a measure of the carbohydrate level and therefore energy stores of a plant. A plant with higher energy reserves is in a relatively high stress tolerance phase while a plant with lower energy reserves is in a relatively low stress tolerance phase. The applicant has found that stress tolerance varies exponentially so there is a fairly sharp threshold at which healthy plants become less tolerant to stress therefore qualitative tests are and have been in the past unsatisfactory in determining this important factor.
Total dissolved solids is determined by juicing a sample of a plant and then measuring the refractive index of the uncontaminated sample. In the case of strawberries, the sample can originate from any part of the plant including the leaves and roots but preferably, the sample is sourced from the crown and in older plants, the sample is sourced from the crown adjacent the top of the crown. The crown or part of the crown can be juiced and the TDS determined and from this, the applicant has devised a method for ascertaining the stress tolerance phase for the plant. The applicant has found the stress tolerance phase determined for a single plant or representative group of plants can be extrapolated to a population of plants which share a common origin and history with the sample plant or plants to obtain an average figure of tolerance and make predictions for the population.
An apparatus suitable for ascertaining the TDS is a refractometer where the refractive index of a juice sample relative to the refractive index of distilled water provides a measure of total dissolved solids and from the following description, it will be seen that the stress level or in the case of transplants, the strike rate is related to TDS is in terms of a logarithmic relationship. Therefore, the present invention includes a direct readout refractometer having a logarithmic scale indication of stress level. Typical quantitative measures that can be used as convenient and direct indications of a populations overall capability of coping with stress is a readout of xe2x80x9cstrike ratexe2x80x9d for transplants, xe2x80x9crecovery ratexe2x80x9d for pruned plants and so forth. The applicant has found that these measures reflect on observable plant characteristics arising in a population following stress and these are related to the TDS measured for the sample plants.
The carbohydrate level may also be ascertained by measuring sugar concentrations in plants, such as by using a near infra-red (NIR) spectrometer to read the concentrations and non-destructively and insitu.